Compensation of unbalance in rotary bodies

ABSTRACT

Unbalance of a rotary body is compensated by removing excess mass by means of an internal milling cutter cutting an eccentrically located groove that merges gradually into the undisturbed periphery of the body. The cutter is mounted on a slide in a frame so that feed advance of the cutter can take place along any predetermined radial direction with reference to the body axis. By turning the slide the groove can be lengthened, by shifting the tool axially the groove can be widened. Alternatively, the cutter can be mounted on a cross-slide system to be ameanable to component control of the feed advance, if the unbalance has been determined in components of ,e.g., an orthogonal coordinate system. Plural milling cutters can work on the same body simultaneously.

United States Patent [191' Reutlinger June 18, 1974 1 1 COMPENSATION OF UNBALANCE IN ROTARY BODIES [75] Inventor: Wolf-Dieter Reutlinger, Darmstadt,

Germany [30] 1 Foreign Application Priority Data June 26, 1972 Germany 2231226 [52] US. Cl. 90/11 C, 90/15 R, 82/DIG. 8, 82/20, 51/73 R, 51/73 GC, 29/1 D [51] Int. Cl. B236 3/06 [58] Field of Search 29/1 D; 82/20, DIG. 8; 90/11 C, 15 R; 51/73 R, 73 GC [56] References Cited UNITED STATES PATENTS 8/1922 Cullen et a1. 90/15 X 2,893,292 7/1959 Naperola 82/20 X Primary Examiner-Francis S. I-Iusar Attorney, Agent, or Firm-Ralf H. Siegemund 57 ABSTRACT Unbalance of a rotary body is compensated by removing excess mass by means of an internal milling cutter cutting an eccentrically located groove that merges gradually into the undisturbed periphery of the body. The cutter is mounted on a slide in a frame so that feed advance of the cutter can take place along any predetermined radial direction with reference to the body axis. By turning the slide the groove can be lengthened, by shifting the tool axially the groove can be widened. Alternatively, the cutter can be mounted on a cross-slide system to be ameanable to component control of the feed advance, if the unbalance has been determined in components of ,e.g., an orthogonal coordinate system. Plural milling cutters can work on the same body simultaneously.

14 Claims, 5 Drawing Figures FATENTEDJUN 1a 1914 3 8 1 FL 149 sum 1 or 2 illlllllllllllflli COMPENSATION OF UNBALANCE IN ROTARY BODIES BACKGROUND OF THE INVENTION The present invention relates to compensation of unbalance of rotary bodies. Balancing rotary bodies generally proceeds in several, sequential steps. In the first step the unbalance is determined with balancing machines (or more correctly unbalance measuring machines"), operating with reference to one or more compensation planes. Particularly, location and size of the unbalance is quantitatively determined. The unbalances, so determined, are compensated in a second step according to which mass corrections corresponding to the measured values are performed in the predetermined compensation plane(s). These mass corrections can be carried out by adding or removing mass increments on a previously determined compensation radius. This first compensation process is generally followed by a second determination of any residual unbalance remaining after the compensation process. If the residual unbalance exceeds the prescribed maximum and permitted tolerance, this unbalance check must be followed by a second compensation process, which is generally followed by a determination of the still remaining residual unbalance etc.

The unbalance data can be determined within a few seconds using conventional measuring methods, but comparatively speaking, the mass compensation takes much longer. The time for the complete balancing process is, therefore, largely determined by the type and preparation of the mass compensation. Depending on the type and design of the rotary body unbalance, correction is performed by adding or removing mass, whereby particularly in large scale production, great importance is attached to mass removal by cutting.

The present invention, therefore, relates particularly to unbalance compensation by means of cutting local excess mass from the body. Nowadays the most frequently used type of cutting mass compensation takes place by drilling in the unbalance resultant axis of the unbalance or in unbalance components (located balancing) along a superimposed (hypothetical) coordinate system. For this purpose, the rotary body is rotated under a drill about its rotation axis in such a way that the unbalance faces the drill bit in the compensation plane to be corrected. Then one or several holes are drilled into the body, the holes or bores being arranged symmetrically relative to the resulting unbalance position whereby the quantity of the material cut corresponds to the measured unbalance, based on the effective compensation ratios.

in the case of an unbalance correction by components the cutting mass compensation is carried out first in one of the component axes; thereafter the rotary body must be rotated in the same compensation plane until the drill is oriented to the second component axis whereupon that unbalance component is also corrected by drilling. On completion of the mass compensation in one compensation plane, the rotary body is rotated about its axis in such a way that the unbalance again faces the drill bit in its second compensation plane. Here again mass compensation takes place by drilling one or more holes, or when balancing in components holes are arranged in relation to two points in this sec- 0nd compensation plane, which points are displaced at a particular angle to one another.

When balancing in more than two compensation planes, e.g., as necessary with crankshafts, the blank may have to be rotated into three or more angular positions; even if balancing is carried out automatically.

This method is not only time-consuming but also has other disadvantages.

To automate such a compensation process, unless compensation can be completed by a single bore, relatively complicated computing circuits are required which can individually determine the mass removed by drilling individual bore, the circuit summates the cut mass as removed from all bores and considers that the compensation radii are reduced by the respective drilling depth. The angular deviation of the individual bores relative to the principle bore on the unbalance resultant must be considered additionally.

A particular disadvantage of compensation by means of drilling holes is that, particularly with rapidly moving parts, annoying whistling sounds may occur. In the case of compensation holes on parts rotating in a liquid sometimes turbulence of the liquid medium can have a disadvantageous effect.

Besides drilling, compensation by milling is also known. Thus, e.g., an elongated slot is often made in the outer periphery of the armature bars in an electro motor. For this, either a side milling cutter is introduced or a groove is cut out, a result of consecutive axial displacement. Due to the geometry of the bars, the possible insertion depth of the cutter is limited, and since milling an elongated slot is possible only to a certain degree (changing the spacings of the preselected compensation planes), milled slots must often be made in several adjacent bars, which is also time-consuming.

Mass compensation by milling poses the same difficulties regarding any automation of the compensation process, because each individual cutting must be evaluated individually for its effects on the remaining mass and on the effective compensation radius, and these individual values must be summated taking into account the angle as varying relative to the unbalance resultant.

Finally, milled slots often lead to noise, whereby as far as electric motors are concerned, noise does not only refer directly to acoustics but also to so-called magnetic noise due to interference in the magnetic flux; oscillatory high frequency impulses are generated in this case, which, in turn, are then noticed as acoustic interference.

To bring about improvements in the compensation by cutting the use of special cutters with a concave geometry has already been proposed. Such cutters can be used indeed to cut a large unbalance mass at the ends of the rotary body without special precautions, e.g., to the armature bars. However, this method has the disadvantage that the cutting speeds are not uniform over the cutter surface; while the outer portion cuts the inner portion presses." This pressing causes a relatively high degree of wear on these expensive tools. This particular method also leads to difficulties when performing a second correction. Furthermore, the shape of the tool becomes so unattractive that this method is called potato cutting."

Mass compensation by means of cutting in the hitherto used form, either by drilling or milling, it is, as

stated, necessary to successively perform mass correction in different planes. However, these successive corrections require significant amounts of time. The simultaneous mass correction in several planes, using the known method, is only possible in exceptional cases. This method can therefore, be safely ignored.

SUMMARY OF THE INVENTION It is the purpose and an object of this invention to avoid the disadvantages of the known methods, and a method and equipment for cutting type unbalance compensation on rotational solids is suggested which is characterized by simplicity, time-saving, easy automation possibilities and the chance to compensate simultaneously in several planes without great expenditure.

The invention is based on the principle of cutting peripheral grooves into a rotary body for unbalance compensation, and assumes that previously an unbalance measurement took place. The invention is characterized in that a groove making tool is moved over an arc whose axis is parallel to the axis of the rotary body but eccentric thereto, and the machining diameter is larger than the diameter of the rotary body at the machining point; the machining feed or advance takes place by parallel displacement of the movement axis of the tool and in a predetermined radial direction. Thus, a groove is produced by carrying out the invention, which groove extends at right angles to the axial direction of tool and blank; the groove extends over part of the periphery and has a depth which decreases azimuthally from the deepest point in the center to both sides. Thus, a groove or slot is formed pointing in the direction of rotation which groove gradually merges into the periphery of the rotary body. Due to the gradual transition, whistling is reliably prevented and as the groove extends azimuthally, magnetic interference in electric motors is also reduced.

Experience has shown that such a slot or groove suffices for unbalance compensation even for electric motors where only a limited cutting depth into the armature is permissible. One should not be limited by the width of the cutting tool; therefore, according to a further development of the invention, the width of the slot can be increased by moving the tool axially during the machining process to widen the groove or the slot. Finally, the rotation axis of the tool can move not only radially but also in an are about the axis of the rotary body during cutting, so that the azimuthal extension of the groove can be controlled without changing the maximum depth. Thus, such a groove has not only transition portions at the beginning and end, but also, a possible long zone of constant depth.

Generally speaking, the following movements and placements are to be distinguished. Beginning with a coaxial disposition of tool and body, the tools axis is shifted and displaced transverse to the body axis, radially thereto. The direction of that radial displacement takes place in the radial direction of the excess-mass unbalance. As the tool rotates on its axis, the simplest form of a balance correcting groove is produced. The radial advance here determines the maximum depth. The axis of the tool can then be turned about the body axis over an arc to lengthen the groove azimuthally without increasing itsdepth; the tool can be shifted axially to widen the groove.

The special advantages of the features of the invention are particularly apparent from the following description of the design of apparatus for performing the method. In its basic design such an apparatus is characterized in that the machining tool for the fixedly held rotational solid has one or several cutting blades or teeth whose mounting can rotate about an axis which is parallel to the axis of the rotary body. The cutting blades are inwardly directed on the rotation axis of their support. The rotatable support for this cutting tool can slide in a frame at right angles to the rotation axis; this frame is rotatable about the axis of the rotary body. That rotation, however concerns only the adjustment of the tool in relation to the direction of the excessmass unbalance.

The preferred embodiment of the invention employs a milling cutter whose cutting blades or teeth are arranged inside of a sleeve so as to act towards the center thereof. The diameter of the addendum line or machining circle of this milling cutter is larger than the external diameter of the rotary body in the machining plane, so that the azimuthal extension of the groove as cut follows indeed a circle of larger diameter than the diameter of the blank. Moreover, the body can be shifted into the sleeve initially in coaxial relation, and the adjustment of the milling cutter into an eccentric position is controlled subsequently so as to obtain the eccentrically located compensation groove in the body.

DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distincly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIGS. 1 and 2 respectively show front and side elevation of an apparatus according to the preferred embodiment of the invention, together with the rotary body to be machined;

FIGS. 3 and 4 are the schematic representation of grooves cut into the body, whereby the cutter was adjusted only radially during cutting in FlG. 3, while there was additional azimuthical adjustment in FIG. 4;

FIG. 5 is a front elevation of a modified apparatus for carrying out compensation cutting.

Proceeding now to the detailed description of the drawings, FIGS. 1 and 2 show a rotary body 1 to be compensated as being clamped to a machine base 3 by means of two clamping jaws 2. A stand or holder 8 is slidably mounted in base 3. The holder 8 is the principle support for a machining tool which is constructed as an internal milling cutter. The cutter has a mounting annulus sleeve or mounting ring 4 for cutting teeth or blades 4a. The blades or teeth are arranged to project inwardly from the mounting ring 4, whereby, however, the diameter of the machining circle 4 b is larger than the external diameter of the rotary body in the machining plane.

The rotary body is placed in an initial position prior to the machining process, in which initial position the rotation axis of the cutter coincides with the rotation axis of the rotary body. Thus, the rotary body can easily be passed through the cutter and then held in the machining position by drawing together the clamping jaws 2. The machine tool art provides further examples of devices for inserting blanks in internal cutters and holding them there.

To perform the compensation process, the internal milling cutter ring 4 is mounted in an easily replaceable manner in a tool holder 5, which, in turn, is rotatably mounted in a sliding carriage 6. Sleeve 5 is driven by the motor 18 and rotates about the axis of the internal cutter for obtaining milling operation. The carriage 6 does not follow that rotation, but serves as stationary support for motor 18.

Sliding carriage 6 is mounted together with the support for tool holder 5 in a frame 7, having guide rails 7a and 7b for permitting the carriage 6 to slide in a direction (axis 6a) transverse to the axis of body 2 as well as transverse to the milling axis. The carriage 6 can be driven for sliding in frame 7 by means of a stepping motor driving a worm gear 10a which, in turn, moves carriage 6 along the said direction or carriage axis 6a. Frame 7 has an internal hub portion 7c for journalling the frame in stand or holder 8. The journal axis for that rotatable support is coaxial with the axis of body so as to permit turning of the frame 7 concentric to and about the axis of body. For simplification purposes in the drawings, the journal is shown as sleeve bearing without constructive details, as the bearing can be designed differently.

Frame 7 together with mounted sliding carriage 6, wherein tool holder 5 is rotatable, may be turned by a servomotor 9 which is constructed as a stepping motor and rotates the sliding carriage axis 6a by the measured angle about the axis of body 1 from an initial position to the unbalance position as had been marked previously on the rotary body. As will be understood shortly, the axis 6a or a projection thereof into the plane of the milling cutter where intersecting the periphery of body, marks the point of maximum cutting action that will take place. Upon turning the frame 7 with glide 6 and milling axis about the axis of body 1, the azimuth of that point is changed and will be adjusted in accordance with the azimuth of the unbalance in body. These adjustments take place while the tool is still concentric to the axis of body 1.

The machining feed of the tool 4 takes place with the aid of the second servomotor 10 which moves sliding carriage 6 and therefore, also internal cutter blades or teeth 4a towards body 1, constituting a blank for this operation. The radial advance of carriage 6 with milling cutter 4, 4a, in frame 7, involves two concatenated distances in each instance. The first incremental distance leads from the concentric position of cutter and body to a tangential arrangement of the machining circle of the cutting teeth or blade with the body. The second incremental distance traversed determines the maximum depth of cutting.

The motor 10 is under control of a circuit 100 which may operate the motor 10 in a quasi closed loop advancing carriage 6, until the teeth or blades 4a contact body 2. This contact can be determined in known manner, for example, by electrical contact read-out or by a torque switch in the cutter drive.

The number of steps of the stepping motor 10 to be performed after contact has been made is determined by the stored measuring signal corresponding to the unbalance magnitude and established previously on an unbalance measuring machine during the previous unbalance measuring sequence, taking into account the non-linearity between the nonuniform groove depth, cut mass and effective compensation radius.

If the greatest possible machining depth is reached then a further compensation can take place by moving the tool in the axial direction which can easily be achieved in the moving stand 8 axially in machine base 3. This way, the groove will be widened.

Finally, it is also possible on reaching a particular machining depth to rotate the frame to one or both sides via stepping motor 9 and, therefore, increase the azimuthal slot length without losing the advantage of gradual transition. In effect, that turns the axis 6a of milling feed advance and the motor 9 should turn in both directions to retain symmetry of the slot in relation to the unbalance direction which coincided with the initial adjustment of axis 6a.

FIGS. 3 and 4 show the slot forms obtained; in FIG. 3, the slot was obtained exclusively by means of a radial movement of the cutter on the previously adjusted but fixed axis 6a. The reference numberal 4c denotes the bottom of the groove cut and the diameter of that bottom circle is determined by the machining circle 40 of the cutter, which is larger than the diameter of body 1. This then accounts for the configuration of the groove with a maximum depth and gradual merging with the periphery of body 1. In FIG. 4a, the slot has resulted from a radial movement of the cutter as before, but additionally the frame 7 was turned over a certain angle a. This way, the azimuthal length of the groove has increased in that there is now a portion of constant depth and the length thereof spans that angle a.

As compensation takes place always with a single slot of the same geometrical shape, it is possible without great effort, using appropriate computing devices, to determine the necessary tool advance, using the measured unbalance value as input and to control from the computer the servomotor 10 for the advance of carriage and milling cutter. Strictly speaking, the depth of cutting would be determined by trial and error, i.e., by altematingly cutting and measuring the residual unbalance. However, it is an advantage of the present invention to permit the unbalance compensation to proceed in a one step process, on basis of previously conducted tests which established a characteristic between unbalance on one hand and needed, compensating groove depth on basis of the eccentric milling on the other hand.

FIGS. 3 and 4 show that the amount of mass removed is very accurately determinable on basis of the milling radius, of the body radius, of the eccentricity of milling circle and body peripheries as adjusted (this is the variable parameter in the process) and, of course, on basis of the groove width as cut by the particular milling cutter teeth.

As shown furtherin FIG. 2, it is easily possible to make use of the invention concurrently in two compensation planes by using two corresponding devices located on both sides of the body to be compensated to simultaneously perform the compensation in the two compensation planes. This is particularly advantageous in the case of mass correction on crankshafts where clue to the angular arrangement of the counterweights, whereon the mass correction must be performed, the feed direction of the cutter relative to the crankshaft as mounted in a particular angular position is fixed from the start. The correction data obtained from the unbalance measurement and related to the individual counterweights and their particular angular position directly control the cutter feed on the feed paths and for distances determined automatically in a computer controller or the like, whereby the feed direction of the individual cutting devices is fixed from the outset by the design of the crankshaft.

Another example for practicing the preferred embodiment of the invention is shown in FIG. 5. This example will find particular utility when the measured values of the unbalance are presented in two, fixed axes, 90 components. According to FIG. 5, two frames 11 and 12 are provided at right angles to one another. The frames are oriented in accordance with the two orthogonal coordinates in terms of which the unbalance is defined. The azimuth of the body as held in the clamp (the same as in FIGS. 1 and 2), is, of course, adjusted as to the orientation of the unbalance data so that the coordinate system inherent in the body as to representation of measured unbalance coincides in the compensation plane with the coordinate system as established by frames 11 and 12. The frame 11 serves as guide rail for a sliding carriage 13, which carries the other frame 12 which, in turn, carries a sliding carriage 14; the latter carriage carries the milling tool 15. Two stepping motors l6 and 17 are arranged on both guide rails, and they are controlled in such a way that the desired slot shape and depths are obtained.

The examples above employ internal milling cutters which represent the preferred embodiment of the invention, but it is also possible to use other circular machining tools such as end mill cutters, planing cutters, etc. Such modifications can result from special forms or dimensions of the blank.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

I claim:

1. A tool for providing compensation of unbalance of a rotary body by selectively cutting material off the body in selected locations in accordance with a previously determined measurement of unbalance, comprismg;

first means for holding the body in a fixed position;

an internal groove cutter with at least one radially inwardly directed cutting tooth operating on a machining circle ofa diameter not smaller than the diameter of the body; second means for mounting the groove cutter in particular axis parallel relative to the axis of the body, and including third means for azimuthally as well as radially adjusting the operational axis of the cutter relative to the axis of the body and in axis parallel relationship thereto, prior to cutting; and

means for advancing the cutter radially towards the body for cutting a groove.

2. Tool as in claim 1, the second means including a stand; a frame journalled on the stand coaxially to the body; a slide carriage on the frame, the groove cutter being mounted on the slide carriage.

3. Tool as in claim 2, the groove cutter being a milling cutter with plural radially inwardly directed teeth defining a machining circle of a diameter larger than the diameter of the body.

4. Tool as in claim 2, the stand being displaceably mounted on a base, for axially adjusting the stand with frame and cutter relative to the body.

5. Tool as in claim 1, the second means including further means for axially adjusting the cutter in relation to the body. A

6. Tool as in claim 1, the third means including a motor for adjusting the distance of the axes from each other, and control means for operating the motor nonlinearly in dependence upon measured unbalance.

7. Tool as in claim 1, the second means including a stand, a first carriage slidably mounted in the stand for sliding in a first direction transverse to the axis of the body, a second carriage slidably mounted in the first carriage for sliding transverse to both, the axis of the body and the direction of sliding of the first carriage; the groove cutter being mounted on the second carriage.

8. Method for compensation unbalance in a rotary body, by selectively cutting the body in selected locations in accordance with a previously determined measurement on unbalance, comprising:

using a groove cutter with cutting teeth defining a machining circle of diameter not smaller than the diameter of the body;

positioning the body in the cutter in eccentric axis parallel relation thereto including azimuthally adjusting the axis of the cutter and the axis of the g body relative to each other; and advancing the groove cutter on a radius relative to the axis of the body so that the cutter cuts a groove into the periphery of the body along an eccentric circle at a maximum depth in accordance with the unbalance measurement.

9. Method as in claim 8, the positioning including adjusting the milling cutter axially with respect to the axis of the body during the cutting operation.

10. Method as in claim 8, the positioning including adjusting the cutter azimuthally as to its axis with respect to the axis of the body during the cutting operation.

11. Method as in claim 8, the azimuthal adjusting of the cutter including adjusting the cutter radially along two different, transversely oriented radii with respect to the axis of the body.

12. Method as in claim 8, wherein the cutting operation is carried out simultaneously in several different planes, using separate cutters for the operation in each plane.

13. Method as in claim 12 for unbalance compensation of multi cylinder crank shafts.

14. Method as in claim 13, the cutting operations as carried out respectively in each of the planes involving individual radial directions corresponding to the respective compensation members of the crank shaft and in the respective compensation planes.

l l l 

1. A tool for providing compensation of unbalance of a rotary body by selectively cutting material off the body in selected locations in accordance with a previously determined measurement of unbalance, comprising; first means foR holding the body in a fixed position; an internal groove cutter with at least one radially inwardly directed cutting tooth operating on a machining circle of a diameter not smaller than the diameter of the body; second means for mounting the groove cutter in particular axis parallel relative to the axis of the body, and including third means for azimuthally as well as radially adjusting the operational axis of the cutter relative to the axis of the body and in axis parallel relationship thereto, prior to cutting; and means for advancing the cutter radially towards the body for cutting a groove.
 2. Tool as in claim 1, the second means including a stand; a frame journalled on the stand coaxially to the body; a slide carriage on the frame, the groove cutter being mounted on the slide carriage.
 3. Tool as in claim 2, the groove cutter being a milling cutter with plural radially inwardly directed teeth defining a machining circle of a diameter larger than the diameter of the body.
 4. Tool as in claim 2, the stand being displaceably mounted on a base, for axially adjusting the stand with frame and cutter relative to the body.
 5. Tool as in claim 1, the second means including further means for axially adjusting the cutter in relation to the body.
 6. Tool as in claim 1, the third means including a motor for adjusting the distance of the axes from each other, and control means for operating the motor nonlinearly in dependence upon measured unbalance.
 7. Tool as in claim 1, the second means including a stand, a first carriage slidably mounted in the stand for sliding in a first direction transverse to the axis of the body, a second carriage slidably mounted in the first carriage for sliding transverse to both, the axis of the body and the direction of sliding of the first carriage; the groove cutter being mounted on the second carriage.
 8. Method for compensation unbalance in a rotary body, by selectively cutting the body in selected locations in accordance with a previously determined measurement on unbalance, comprising: using a groove cutter with cutting teeth defining a machining circle of diameter not smaller than the diameter of the body; positioning the body in the cutter in eccentric axis parallel relation thereto including azimuthally adjusting the axis of the cutter and the axis of the body relative to each other; and advancing the groove cutter on a radius relative to the axis of the body so that the cutter cuts a groove into the periphery of the body along an eccentric circle at a maximum depth in accordance with the unbalance measurement.
 9. Method as in claim 8, the positioning including adjusting the milling cutter axially with respect to the axis of the body during the cutting operation.
 10. Method as in claim 8, the positioning including adjusting the cutter azimuthally as to its axis with respect to the axis of the body during the cutting operation.
 11. Method as in claim 8, the azimuthal adjusting of the cutter including adjusting the cutter radially along two different, transversely oriented radii with respect to the axis of the body.
 12. Method as in claim 8, wherein the cutting operation is carried out simultaneously in several different planes, using separate cutters for the operation in each plane.
 13. Method as in claim 12 for unbalance compensation of multi cylinder crank shafts.
 14. Method as in claim 13, the cutting operations as carried out respectively in each of the planes involving individual radial directions corresponding to the respective compensation members of the crank shaft and in the respective compensation planes. 